Potentiometer



y 1934- R. K. WINNING. ET AL ,960,611

POTENTIOMETER Filed July 11, 1931 lNVE TOR5 fi mw M m ATTORNEYS Patented May 29, 1934 POTENTIOMETER Robert K. Winning, Wauwatosa, and Emil Sinner, Milwaukee, Wis., assignors to Clum Manufacturing Company, Milwaukee, Wis., a. corporation of Wisconsin Application July 11, 1931, Serial No. 550,158

4 Claims.

This invention relates to improvements in potentiometers.

The objects of the invention include the provision of a novel inexpensive heat dissipating I form of potentiometer which can be subjected to heavy currents without burning out.

It is a further and very important object of the invention to provide a potentiometer adapted for single hole mounting and so designed that the moving contact is insulated from the mounting member, the latter being connected with one end of the resistance whereby to ground the resistance through a metal panel automatically upon the mounting of the instrument.

In the drawing:

Figure 1 shows a rear elevation of a device embodying the invention.

Figure 2 shows the front elevation of the device with the mounting sleeve and control Ishaft cut away in transverse section.

Figure 3 is an enlarged view of the parts as they appear in a section taken generally in a plane including the axis of the control shaft as indicated by line 3-3 in Fig. 2. 7

Like parts are identified by the same reference characters throughout the several views.

The potentiometer is particularly adapted for use in the circuit disclosed in the co-pending application of F. J. Pease No. 531,079 filed April 18, 1931 and entitled Generator control. It has utility in other fields however, and therefore the following disclosure is confined to the construction and operation of the device per se.

The instrument is assembled upon a mounting sleeve 4 which 'is exteriorly threaded and proportion 9 apertured to receive the mounting sleeve and to which the mounting sleeve is riveted.

Mounted on the base plate 8 is an annular strip 10 of dielectric material in the form of a split ring having its ends held to the plate by contact terminal rivets 11 and 12, the latter of which is grounded to the plate as shown in Fig. 2. Rivet 11 is insulated from the mounting plate 8 by means of the split ring 10 at the rear 5 of the plate and a sheet 13 of dielectric material at the front of the plate which also serves to insulate an intermediate contact rivet 14.

Each of the terminal rivets is internally tapped to receive a screw 15 whereby wiring may be properly connected with the terminals of the device. No wiring will ordinarily be necessary for connection to terminal 12, however, providing panel 7 is grounded, for this terminal rivet is in direct electrical connection F through the frame plate 8 and mounting sleeve 4 with panel 7.

Mounted on the dielectric ring 10 is a toroidal resistance coil 20 which is preferably made of relatively stiif insulated resistance wire so that it will hold its predetermined toroidal form with only such support as is provided by the internal annular dielectric strip 10. The ends of the wire are connected to terminals 11 and 12 as shown at Fig. 1 whereby one end of the resistance element is grounded and the other insulated.

It is not essential that the wire used in the device should be insulated wire, but it is found that the insulation on the wire not only protects the device against grounding through contact with other electrical parts, but also ensures accurate spacing from each other of successive coils of the toroidal resistance element.

Contact surfaces on successives coils are provided by abrading or otherwise removing the insulation along a narrow path at 21 in the inner periphery of the coil.

Engaged by the central terminal rivet 14 is a metal brush member 22 apertured at 23 to avoid contact with the operating shaft 25, which is journaled in sleeve 4. The brush is secured against displacement by an integrally formed tongue 26 fixed in an aperture in the dielectric sheet 2'7 used as insulation on the back side of the instrument. This piece of fiber in turn is engaged by a tongue 28 on the mounting plate 8. The tongue 26 of the brush is protected against grounding by the provision of a large opening at 29 in the mounting plate 8.

The brush 22 establishes electrical connection between the central terminal rivet 14 and the moving contactor 30 of the potentiometer. This contactor comprises a spring arm which is mounted to turn with shaft 25 but is insulated therefrom. It is supported from the shaft by a dielectric disk 31 splined to the flattened end portion 32 of the shaft and notched at 33 and 34 to receive integral portions of the contactor 30. A central opening through the contactor is sufiiciently large to avoid all metallic connection with shaft 25.

Likewise splined to shaft 25 is a washer 35 which is insulated from the brush 22 by an interposed dielectric gasket 36. The washer provides a thrust bearing against the mounting plate and has upset tongues 37 adapted to engage the mounting plate and thereby to limit the rotative movement of shaft 25. The parts are maintained in frictional pressure engagement by the riveted end portion 39 of shaft 25 which is upset on a washer 40. A split ring 41 on the shaft engages the outer end of the mounting sleeve 4 thereby drawing the mounting sleeve and the mounting plate 8 against washer 35 and the rotative parts between said washer and the upset end portion 39 of the shaft.

When the shaft is rotated the moving contactor 30 establishes electrical connection with successive coils of the toroidal resistance 20. The pressure of the contactor is absorbed directly in the supporting annular strip 10. Thus, although the toroidal resistance element is adequately supported against the radial pressure of the spring contact finger, its side portions are left wholly open for the circulation of air whereby heat generated by the flow of electricity through the resistance wire is dissipated without developing excessive temperatures.

Although a metal shaft may be used for actuating the moving contactor of the potentiometer, the contactor is fully insulated from the shaft and the shaft, instead of being grounded to said moving contactor, as is usual practice, is grounded to one end of the resistance element.

The resiliency obtained by the cup-shaped e1n bossing 9 of the mounting plate ensures a permanence of the pressure produced in the rivet of the shaft upon the moving parts of the device, whereby said parts will always be subject to sufficient resistance to ensure the maintenance of a given setting. Friction takes place between the fixed mounting plate 8 and the fixed brush 32 on the one hand, and those parts on the other hand which rotate with the shaft, including washer 35, dielectric disk 36, contactor 30, dielectric mounting 31, and washer 40.

We claim:

1. A resistance device oomprising a mounting member, a shaft supported for rotation therein, an annular strip connected with said mounting member and disposed in a plane at right angles to said shaft, a resistance element comprising a toroidal coil of resistance wire mounted on said annular strip, and a moving contactor supported from said shaft and including a finger engageable with successive turns of said coil in opposition to the inner margin of said annular supporting strip, whereby said coil is supported against the pressure of said contact finger while its turns are exposed for air circulation and heat dissipation.

2. A resistance device comprising a mounting member, a shaft supported for rotation therein, an annular strip connected with said mounting member and disposed in a plane at right angles to said shaft, a resistance element comprising a toroidal coil of resistance wire mounted on said annular strip, and a moving contactor supported from said shaft and including a finger engageable with successive turns of said coil in opposition to the inner margin of said annular supporting strip, whereby said coil is supported against the pressure of said contact finger while its turns are exposed for air circulation and heat dissipation, said resistance element comprising insulated wire having its surface bared about the inner periphery of the toroidal coil in the path of movement of said finger.

3. In a device of the character described, the combination with a metallic bearing and means for mounting said bearing on a metal panel in electrical contact therewith, a metal mounting plate secured to said bearing, a resistance coil supported by said plate and having one end electrically connected therewith and the other end insulated therefrom, a shaft journaled in said bearing, a contact slidably engaging said coil and rotatable by means of said shaft, said contact being insulated from said shaft and a brush carried by said plate and contacting said contact, said brush being insulated from said plate.

4. In adevice of the character described, the combination with a rotatable metal shaft, of a metal bearing for the shaft provided with a threaded exterior surface, metallic nuts on said exterior surface adapted for clamping engagement with a metal panel, a metal supporting plate secured to said bearing, a contact disk secured to said shaft and contacting said plate, an insulating disk adjacent said contact disk, a contact brush surrounding said shaft and spaced therefrom, a contactor arm having a portion surrounding said shaft and spaced therefrom, said portion being in frictional contact with said brush, an insulating mounting secured to said shaft and said contact arm portion, whereby upon rotation of said shaft the contact arm will be rotated therewith, a resistance coil arcuately disposed about said shaft and with which said contact arm is engaged for sliding contact thereon, a terminal for one end of said coil supported by and insulated from said mounting plate, a second terminal for the other end of said coil supported by and contacting said mounting plate, a third terminal for said brush mounted on and insulated from said mounting plate.

ROBERT K. WINNING.

' EMIL SINNER. 

